Apparatus for the production of building units from afterhardening materials

ABSTRACT

The invention relates to an apparatus for the production of building units from an afterhardening mixture containing cement and/or lime as binding material. The raw mixture is continuously fed and pressed by stamping into a die with CO 2  gas at a pressure higher than atmospheric being passed through the raw mixture in the die space. Through an instantaneous reaction of carbonation, the material is hardened to a formed body. The CO 2  gas is prevented from escaping by a gastight seal in the vicinity of the inlet port of the die. Further towards the outlet port, the pressure of the CO 2  gas is decreased. In the vicinity of the outlet port only as much CO 2  gas is fed as is necessary for the completing of the chemical reaction. Thus, any loss of gas will be minimized. The continuously discharged body is cut to size by using a saw.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention realtes a process for the production of bodies, especiallybuilding units from afterhardening materials containing hydraulicbinder, particularly cement as setting agent.

Such building unit production methods are known, at which hardening ofthe cement-set moulded material is accelerated by injection of CO₂ gasinto the raw mixture (e.g. U.S. Pat. No. 4,093,690). These methods arebased on carbonation, i.e. a process when the large amount of Ca(OH)₂compound present in the cement mortar quickly changes over to limestoneupon the effect of CO₂ gas. The limestone molecules being formed duringthis process, become so tightly bonded to each other that the product,e.g. building panel may reach even 35-50% of its 28-day-strength in 5-30minutes, though hydration of the binding material, e.g. cement has noteven begun.

The carbonation takes places generally in a closed space containing theraw mixture to be set with cement by producing differential pressure,then a pressure exceeding the atmospheric one is brought about with theinjection of CO₂ gas, as a result of which the CO₂ gas may penetrateinto the pores of the raw mixture and chemical reaction takes place. Theraw mixture is filled into a mould determining the shape of the productto be produced and compacted, then placed into a closed space togetherwith, or removed from the mould. These methods, however, are fairlycostly, because the closed spaces require careful sealing to be realizedwith difficulty and at high cost. Apart from this, the alternating useof vacuum and high pressure is lengthy, thus, the techologies allowingonly a step by step production carried out with several operations(filling into the mould and compacting; filling and discharging thecarbonation space; carbonation) take fairly long time.

A building unit production technology combined with carbonation isdescribed in the Hungarian patent specification No. 189.455 whereelastic fibrous material as additive is used for the preparation of thecement-set raw mixture, and there is utilized the characteristic featureof this mixture for more or less elastic reversion after compaction,thus, its volume expands when &he compressive force is stopped duringthe setting time of he hydraulic binding material, i.e. cement. The rawmixture placed between two press-plates is compressed in a greaterdegree in the vicinity along their flanges than the rest of themixture--either by using a thicker part along the flanges of thepress-plate or by applying a locally greater amount of rawmixture--thus, a strip of higher density, consequently of lower gaspermeability is formed at the flanges, than within. This strip of higherdensity along the flanges functions as a seal, and prevents the CO₂ gasinjected for carbonation from escaping from the mixture on the sides.Although this method is more favourable than the former ones itsdrawback resides firstly in its periodicity, thus in its relatively lowproductivity and in the fact that a solid end-product can be producedonly from mixtures containing elastic fibrous material.

The invention aims at providing a process for the production of bodies,particularly building units from an afterhardening material byaccelerating the setting with carhonation, which partly allows acontinuous production thereby considerably improving the productivityand economic efficiency, and partly it is not restricted to the use ofafterhardening mixtures prepared with an elastic fibrous additive as astarting material (to be moulded), whereby it substantially extends thechoice of products to be economically produced with carbonation.

The invention is based on the recognition that when the afterhardeningmaterial is passed through a moulding space open at both ends, andescape of the CO₂ gas is prevented by a continuous mechanical compactionof the raw mixture in the vicinity of the point of inlet and by reducing&he pressure of the CO₂ gas to a minimum--in the given case to theatmospheric pressure--in the vicinity of the point of outlet, and theCO₂ gas is injected between these two points into the mould space evenlydistributed along the mould face(s), however under a pressure reducedfrom the inlet towards the outlet, the production may be madecontinuous, and the product emerging from the mould space will appear ina solid, moulded state as a result of carbonation taking place in themould space.

On the basis of this recognition, the problem was solved by a processaccording to the invention, in the course of which the still nothardened mixture is admitted into the mould, where carbonation reactionis brought about by injection of CO₂ gas into the mixture, and therebythe mixture is hardened, said process comprising the steps of pressingthe afterhardening mixture continuously through the mould space open atboth ends, while CO₂ gas is injected into the material under pressurereducing from inlet port of the material toward the outlet port of thehardened body, and creating a quasi gastight layer from theafterhardening material with mechanical compaction in this mould spacein the vicinity of the inlet port and bringing about a quasi-gastightcondition between this layer and the mould surfaces, and in the vicinityof the outlet port inJecting as much amount of CO₂ gas into the mouldspace as necessary for the complete, or essentially complete chemicalreaction of carbonation. The afterhardening material is stamped-pressedinto the mould space preferably with a reciprocating device.

Expediently, the CO₂ gas is injected into the mould space through atleast one of the confining surfaces under pressure exceeding theatmospheric pressure; and when passed throug the afterhardening materialthe gas of reduced pressure and quantity is discharged from the mouldspace through at least another mould face, and/or vacuum is applied toat least one face of the mould space, and this way the CO₂ gas is madeflown through the material, or its flow is intensified.

According to another advantegeous feature of the invention, in a zonefollowing the compacted layer of material in the vicinity of the inletport, CO₂ gas at a pressure of suitably 3-6 bar is injected into thepores of the mixture then--looking in the direction of the material'smovement--in a second zone, where the instantaneous explosion-likereaction of carbonation takes place, CO₂ gas under a lower pressure ofe.g. 2-3 bar is injected into the material, the quantity of which isessentially the same as that of the CO₂ gas consumed by the reaction,whereby the carbonation reaction is continued, then in a third zone CO₂gas under even lower pressure of e.g. 1-2 bar is injected into the mouldspace, whereby essentially full completion of the carbonation reactionis realized. A further embodiment of the process is characterized bycreating a balancing zone in the mould space situated directly behindthe outlet port of the material hardened by carbonation, where the gasoutflow is checked, and in the zone(s) behind the balancing zone, gas isinjected as a function of the quantity of the outflowing amount and/orpressure of the gas. It is generally advisable to cut to size--suitablyby sawing--the carbonation-hardened body leaving the mould space, and toinject the CO₂ gas into the mould space with a gas mixture, containingsuitably at least 30% of CO₂ gas.

It may he advisable to inject the CO₂ gas into the raw mixture prior tofeeding it into the mould. The setting process can be accelerated bythis carbonation pretreatment.

The apparatus according to the invention contains a mould, a CO₂gas-source, e.g. gas bottle and openings e.g. holes in at least one wallof the mould, suitable for injection of CO₂ gas into the mould space,the pressure of which exceeds the atmospheric pressure, and thisapparatus is characterized in that the mould has an inlet port forfeeding in the raw afterhardening mixture and an outlet port fordischarging the body hardened by carbonation; a press mechanism situatedin front of the inlet port for pressing the raw afterhardening mixtureinto the mould space, and moving the afterhardening mixture and the bodyhardened therefrom by carbonation through the mould space; and the holesleading into this mould space and used for injection of the CO₂ gas aredivided into separate hole groups communicating with devices suitablefor injecting CO₂ gas, at pressures to be separately controlled for eachzone. It is expedient when at least one wall of the mould is providedwith holes for outlet of the CO₂ gas remaining--in given case--after thecompleted chemical reaction of carbonation, which holes are expedientlycommunicating with pipes connecting the CO₂ gas source, e.g. gas bottlewith the mould plate containing the holes for injecting CO₂ gas into themould space.

An embodiment of the apparatus is characterized by having a forward pipefor feeding the CO₂ gas into the mould space and a return pipe forfeeding back into the forward pipe the CO₂ gas remaining--in a givencase--after the completed carbonation reaction; a gas pump beingconnected to the forward pipe into which also the return pipe isleading, and--in up-stream direction of the gas flow--a pipe containingshut-off means, leading out of the CO₂ gas supply source, e.g. gasbottle being joint to the return pipe before the pump, and the forwardpipe being interconnected through leg pipes containing valves withseparate hole groups on the gas inlet side, while leg pipes containingsimilarly valves and leading from the hole groups into the return pipeare provided for discharging the gas remaining--in a given case--afterthe completed carbonation reaction. A vacuum pump can be inserted intothe return pipe.

According to a further feature of the invention the hole groups on boththe gas inlet side and the remaining gas outlet side is leading intoseparate closed chambers fitted expediently gastight to the outer faceof the mould plates. Furthermore it may be of advantage, when the holegroups are leading from--e.g. meandering--ducts running inside the mouldplates into the mould space, each duct communicating with one of the legpipes emerging from the forward pipe or with one of the leg pipesleading into the return pipe.

According to another embodiment of the apparatus given by way ofexample, a device, e.g. a saw suitable for cutting up thecarbonation-hardened body emerging from the mould space is arrangedbehind the outlet port of the mould.

According to another arrangement of the invention, chambers covering atleast one of the hole groups are fitted to the outer side of the mouldplates in the vicinity behind the outlet port of the mould, and gasoutlet stubs containing control valves are leading out of the chambers.

A further embodiment of the apparatus is characterized by providing apress mechanism with a reciprocating beater, e.g. a piston, the crosssectional shape and size of which are the same or essentially the sameas those of the mould's inlet port. In this case it is expedient, whenthe position of the mould and the path of the piston are vertical, thepiston is fitted between guide rails, the guide rails are covered by abell-shaped protective cover, the lower flange of which is running inthe vicinity of the lower edge of the guide rails and a gap is providedfor between said lower flange and the guide rails; and the actuatingmechanism together with the protective cover is situated in a hopperserving for feeding the raw afterhardening mixture into the mould, thehopper leading into the upper end of the mould space.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in further details on the basis ofthe attached drawings illustrating a preferred embodiment of theapparatus by way of example, some of its structural details, graphs inconnection with the exemplified process variants furthermore some of thebuilding units producible with the method according to the invention, asfollows:

FIG. 1 is a schematic vertical cross section of the apparatus;

FIG. 2 a horizontal section along line A--A according to FIG. 1;

FIG. 3a an embodiment of one of the mould plates drawn to a largerscale, showing the sectional view along line B--B according to FIG. 3 ;

FIG. 3b a view from the direction of arrow C, marked in FIG. 3a;

FIG. 4 a graph illustrating the change of the pressure and the body'sdensity within the mixture as a function of the time, taking placeduring compression of the afterhardening mixture prepared withnonelastic additive;

FIG. 5 a characteristic curve related to the afterhardening mixture,same as the one shown in FIG. 4, but prepared with elastic additive;

FIG. 6 a set of curves formed by the curves as shown in FIG. 4,illustrating the result of quickly repetetive compression processes;

FIG. 7 a set of curves different from the one shown in FIG. 6 in that itis formed by the curves shown in FIG. 5;

FIG. 8 a diagram showing the gas pressure, path and time;

FIGS. 9a-9f building units of different cross sectional shapes preparedwith the method according to the invention, to illustrate the extensiveapplicability of the invention;

FIG. 10 a production model of the building unit shown in FIG. 9fproduced with carbonation method according to the invention.

The apparatus shown in FIGS. 1 and 2 contains a mould designated as awhole with 1, a hopper 2 and a press mechanism 3 which in the presentembodiment, comprises a piston 8 moving up and down as indicated by thedouble arrow b, having an expanding neck-part, an actuating mechanism(no shown), and vertical guide rails 9 on both sides of the piston 8 forguiding it while moving up and down.

The mould space 5 of the mould 1 is confined by vertical mould plates4a, 4b of width s (FIG. 2) situated at a distance a from each other(FIG. 1) and by similarly vertical, narrow walls (not shown)perpendicular to the mould plates; the apparatus according to FIGS. 1and 2 is namely used for the production of building panels 22 ofthickness a, whose width perpendicular to the plane of the drawing(FIG. 1) is determined by the width of the mould plates 4a, 4b meassuredin the same direction (value s in FIG. 2), whereas their otherdimension, e.g. the length in the plane of the drawing (FIG. 1) mayoptionally be selected between practical limits. The mould 1 is open onits top and bottom; the inlet port of the mould is marked with referencenumber 6, and its outlet port with 7. The hopper 2 (feed hopper) isleading into the upper open end of the mould 1, and the piston 8 in thehopper fits into the inlet port 6 of the mould 1, i.e.: its crosssectional shape and size are essentially identical with, suitablysomewhat smaller than those of the outlet port 6.

A bell-shaped protective cover 10 with its open end 10a turned down isarranged in the hopper 2 above the mould 1, which covers the guide rails9 and whose lower flange is running in the vicinity of the lower ends ofthe vertical guide rails 9 The protective cover 10 is situated at adistance from the inner surface of the hopper 2 as well as from theouter surfaces of the guide rails 9, and its outer surface is suitablycurved thereby facilitating downward movement of the raw mixtureadmitted in the direction of arrows c toward the inlet port 6 in thehopper 2.

The apparatus includes a gas tank 14 shown in FIG. 1, containing CO₂ gasat a pressure exceeding the atmospheric pressure, said gas tank beingconnected through an intermediate pipe 15 fitted with a shut-off means15a to the return pipe 18 leading to the circulating gas pump 16. Fromthe gas pump 16 a forward pipe 17 is leading out from which leg pipes17a-17c are branching off fitted with valves 17a'-17c'. The leg pipes17a-17c are leading into distribution chambers 23-25 situated along themould plate 4b above each other, one of their confining faces beingformed by the outer side of the mould plate itself, and the chambers23-25 are separated from each other by--expediently gastight--sealings31. A further chamber 26 is arranged below the chamber 25, beingseparated from this latter similarly by sealing 31, and having adeaerating and gas pressure compensation stub leading out therefrom andfitted with valve 21a.

Four chambers are adjoining also the outer surface of the mould plate 4amarked--going downwards from the top--with reference numbers 27-30. Legpipes 18a-18c are leading out from the chambers 27-29, a manometer 19and one of the valves 18a'-18c being built in each of the leg pipes. Theleg pipes 18a-18c are connected to said return pipe 18 in which a vacuumpump 32 is inserted. A deaeration and gas pressure compensation stub 20fitted with valve 20a (control valve) is leading out of the lowestchamber 30. The chambers 27-30 are also separated from one another bysealings 31.

Holes 12 are passing through the mould plates 4a, 4b as clearly shown inFIG. 2, while the same holes are illustrated with dotted lines inFIG. 1. Thus, the holes 12 establish gas passage connection between themould space 5 and the chambers 23-26 and chambers 27-30, respectively(only chamber 23 is shown in FIG. 2).

The mould 1 is divided into technological zones designated--goingdownwards from the top--by I-IV, each comprising a pair of chambers 23,27; 24, 28;, 25, 29; and 26, 30; the function of these zones will bedescribed further in the part dealing with operation of the apparatus.

The gas can be injected into the mould space 5 not only as shown inFIGS. 1 and 2 but also with the structural solution shown in FIGS. 3a,3b. In this case, the mould plates 4a, 4b contain a duct system formedaccording to the said technological zones I-IV. The uppermost zone I hastwo, and each of the zones II-IV has one meandering hole group 11 fortransmitting the gas, whose holes 12 are leading out similarly from ameandering gas distributing duct 13, and which are running in theinterior of the mould plate 4b. (For the sake of better overview, onlyfour holes 12 leading into the mould space 5 are shown in FIG. 3a). Eachgas distribution duct 13 has an inlet stub 32 connected to one of theleg pipes 17a . . . 17n (in the present example to leg pipe 17aaccording to FIG. 3a) leading out of the forward pipe 17. Naturally,valves 17a'-17n' are installed in each leg pipe to adjust independentlythe gas pressure of CO₂ flowing out of each hole group 11. Duct and holesystems identical to those in FIG. 3a, 3b, are to be provided for in themould plate 4a, where the return pipe 18 for each hole group isconnected to the leg pipes 18a-18n.

The chambers 23-26 and 27-30 in FIGS. 1 and 2, as well as the holegroups 11 connected to independent gas pipes according to FIGS. 3a 3boffer the possibility to inject the CO₂ gas into the mould space 5 inthe locally determined zones under different pressures.

Production of the building panel with the apparatus according to FIGS. 1and 2 (as well as FIGS. 3a, 3b) is carried out as follows:

The afterhardening raw mixture containing cement as binding material isled into the hopper 2 at a steady rate and continuously according toarrows c shown in FIG. 1. The afterhardening material passes downwardsto the inlet port 6 of the mould 1. The piston 8 is kept inreciprocating motion as indicated by the double arrow b. The piston 8performs about 15-300, mainly 100-150 compression steps per minute, i.e.the up-and-down motion of the piston is variable--depending on thebuilding unit to be produced and/or on the basic material--within widelimits and it may also be very fast. The cover 10 prevents the rawmixture from passing to the upper end of the guide rails 9, which wouldcause troubles in or inhibiting the run of the piston 8 pressing theafterhardening material from the hopper 2 in between the mould plates4a, 4b, i.e. into the mould space 5. As a result of this pressing in,density of the raw mixture increases--due to the relaxation--to themultiple of the value preceding its compression. Part-quantities of thematerial in proportion with the stroke of the piston 8 fill up the mouldspace 5, and the carbonated cement-set material treated with CO₂ gas (orwith the CO₂ component of a gas mixture) while passing through, leavesthe outlet port 7 of the mould 1 in a hardened condition continuously.

The above production technology to be described subsequently in detailincluding its phases is enabled by the factors as follows:

the cement-set raw mixture--prepared practically by any additive--isalways of a porous texture. Extent of the porosity depends on themeasure of additive components of the mixture (e.g. size of grain and/orfibre) and on the compression. Porosity means that the mixture ispermeable to gas and this feature has an important role in thecarbonation, because the CO₂ gas can only be injected in a gas-permeablecomposition of materials;

the highest internal pressure (stress) in the mixture arises in thevicinity of the inlet port 6 of the mould 1, dropping as continuouslygoing downwards in the mould space 5. As a result of the said maximuminternal pressure, the material will become quasi gastight to such anextent, that the CO₂ gas injected into the mould space 5 can not escapefrom the mould through the inlet port 6. In other words: the gastightcondition of the product is ensured by its still unhardened, but alreadycompacted material.

Returning to the description of operation of the apparatus according toFIG. 1, the material passed downwards by the piston 8 through the mouldspace 5 is treated in the technological zones I-IV, the carbonationtaking place mainly in zones I-III.

By stamping in the material in the uppermost part of the zone I in thevicinity of the inlet port 6, a quasi gastight condition is broughtabout in the material--as referred to above--i.e. mechanically byutilizing also the relaxation force of the compressed material, the CO₂gas injected into the material in the mould space 5 is prevented fromescaping through the chamber 23 and the holes 12 (see also FIG. 2).(Since both the feeding of the raw mixture and stamping-pressing arecontinuous, the quasi gastight core is constantly present in the upperpart of the mould during the whole process of production, by way ofcontinuous reproduction). Effect of the mechanical compaction (though ata downwardly decreaseing extent) extends to the whole zone I, the valueof the relaxation force is high, thus, a fairly high gas pressure and/orthe use of vacuum from the wall 4b of the mould are required forinjecting the CO₂ gas into the pores of the raw mixture; so to say theCO₂ gas has to be pressed into the pores of the mixture. The requiredgas pressure, e.g. 6 bar can be set with the valve 17a' (FIG. 1). Theefficiency of injecting the CO₂ gas into the mixture can be improved byusing the vacuum pump 32; in this case the valve 18a' is open. Thepressure conditions of the gas flowing through can be controlled withthe manometer 19 built into the leg pipe 18a' and the valves 17a', 18a'are adjustable as necessary. By use of a vacuum of e.g. 0.5 bar adifferential pressure is brought about on the inner faces of the mouldplates 4a, 4b, whereby the transversal gas flow from the mould plate 4btowards the mould plate 4a will obviously become more intensive, and thepores of the mixture will evenly be filled with CO₂ gas in the wholecross section.

The pores of the mixture in zone I will be filled up with CO₂ gas, whilethe unnecessary gas of lower pressure (e.g. 3 bar) entering the chamber27 through the holes 12 of the mould plate 4b returns through the legpipe 18a and the return pipe 18 into the gas cycle. Directions of thegas flow through the pipes shown in FIG. 1 are marked with arrows, whilepath of the gas passing from the leg pipe 17a into the chamber 23 inFIG. 2 is marked by arrow e, and the path of the gas flowing through theholes 12 into the mould space 5 is marked by arrow f. The same marks eand f were used in FIGS. 3a and 3b accordingly. It is noted that the gasinjection method according to FIGS. 3a, 3b offers the possibility thatit is sufficient to inject gas under a lower pressure, e.g. 5 bar in&o&he mould space 5 through the second hole group 11 from above (FIG. 3)in the lower range of zone I, where the compacting effect of the piston8 is less effective and -he material has a less density (the internalstress of the compacted mixture--as referred to--is at a maximum on theupper end of the zone I, then it gradually drops when going downwars);in this case, the pressure of the remaining discharge gas is about 2-3bar. In any case, the pressure of &he CO₂ gas injected into the zone Ihas to be selected so as to prevent it from escaping through thecompacted layer of material situated above the zone I in the vicinity ofthe inlet port 6 of the mould 1. Since a quasi gastight condition existsalso between the inner faces of the mould plates 4a, 4b and the mixture,the CO₂ gas can not escape from the mould space 5 along the mould plateseither. Injecting the gas into the zone I under two different pressureshas the further advantage that the low-pressure gas cannot flow frombelow upwards to the inlet port 6, because this is prevented by thehigher pressure gas forcing the low pressure gas towards the oppositemould plate 4a, i.e. to a transversal passage through the mixture.

The chemical reaction between the CO₂ gas and the cement--i.e. thecarbonation--just begins in zone I, but it takes place explosion-like(instantaneous reaction) in zone II. The chemical reaction consumes theCO₂ injected into the zone I, the pressure drops, and vacuum woulddevelop in the material unless the CO₂ is replaced. Therefore,continuing the injection of CO₂ into the zone II through the leg pipe17b and the chamber 24, the CO₂ gas consumed in the zone I during thechemical reaction, is replaced. In zone II, the CO₂ gas is injectedunder a lower pressure still exceeding the atmospheric one e.g. at 4 bar( it is unnecessary to press the gas under into the pores of themixture, at a higher pressure), which flowing through the material,passes into the chamber 28 under a pressure not more than about 2 barand returns to the gas cycle through the leg pipe 18b and the returnpipe 18. By correct adjustment of the valve 18b', vacuum can be appliedalso in the zone II, but this is not essential.

Hardening of the mixture begins at a lesser extent already in zone I,while in the zone II its intensity completely stops the relaxationforce. Thus, the building panel 22 (FIG. 1) in state of hardening iscapable to pass downwards in the mould 1 unobstructed and continuously,the material is not pressed against the walls of the mould as in theupper part of the zone I (where the compressive force produced by thepiston 8 forces downwards the still unhardened raw mixture). As a resultof the chemical reaction of carbonation, vacuum will develop in thematerial.

The pressure of the CO₂ gas injected into &he zone III is furtherreduced, gas at a pressure of e.g. 1 bar is fed thereto. The carbonationprocess in this zone is practically completed. The amount of the gasadmitted to the zone III shall cover the still missing gas required forthe whole carbonation reaction. This way, the detrimental loss of CO₂--adversely influencing the economic efficiency of the process--can beprevented at the lower end of the mould space 5, i.e. at the outlet port7, where the compressed, already carbonated partly hardened materialpasses into the open air, merely by bringing about appropriate pressureconditions in the zone III, in other words: here is fed only a minimumamount (pressure) of the CO₂ gas. The pressure of the remaining CO₂ gasflowing into the chamber 29 (if no vacuum exists) is not much lower thanthe pressure of the admitted gas, e.g. 0.8-0.9 bar. Thus the carbonationreaction is safely completed. It is noted, that a vacuum of e.g. 0.5 barcan be brought about with the pump 32 also in the zones II and III inorder to intensify the transversal gas flow in the chambers 28, 29.

Zone IV is a balancing zone where no CO₂ gas is fed to, here practicallyno chemical reaction takes place. Into the chambers 27 and 30 the CO₂gas flowing eventually hereto along the mould plates 4a, 4b flowsoutwards from within the amount and pressure of which were selected inthe zone III so as to be sufficient for completing the carbonationreaction. If the pressure of gas was correctly selected in the zone III,the gas should just blow out through the control valves 20a, 21a. Thus,with the aid of these control valves 20a,21a the pressure of the CO₂ gascan be balanced in the zone IV. Consequently the production technologydoes not entail any overconsumption consumption of CO₂, becausepractically no perceptible amount of gas escape either on the top or thebottom of the mould 1, which is a significant factor for the economicefficiency.

If, however not pure CO₂ gas but a gas mixture was used for thecarbonation that contains CO₂ only in part (e.g 30%), the neutral gascomponent(s) is (are) not used up for the carbonation reaction, and inthis case the amount of gas (air) emitted through the control valves20a, 21a may also be fairly large, and in this case the valves 20a, 21afunction as air vent.

Athough the individual phases of the carbonation process are realizedseparately from one another in space and time, the whole process ofproduction is continuous, since the material to be moulded and hardenedto building panel passes through the mould space 5 continuously. Thebuilding panel 22 discharged continuously in infinite length through theoutlet port 7 is cut to size by the transversal saw 21 its operationbeing synchronized with the pressing rate, thus, there are obtainedpartially hardened building panels--having e.g. a strength representingabout 30% of the 28-day-strength which can be further cured--by anyknown method--by artificial ageing of by allowing to stand.

Cross section of the building panel 22 produced with the apparatusaccording to FIGS. 1 and 2, is shown in FIG. 9a but it is easilyconceivable that with the aid of the process and apparatus according tothe invention, any optional cross section of the building units can beproduced--within practical limits--by an appropriate selection of thecross sectional shape of the mould space and the piston. Cross sectionof the building unit 30 according to FIG. 9b is wedge-shaped, while thebuilding unit 31 shown in FIG. 9c is of wavy-sgape. A trapezoid buildingunit 32 is shown in FIG. 9d. In fact, the production of a hollowbuilding unit is also possible with the aid of the invention. Theelement 33 shown in FIG. 9e has an annular cross section whose circularhole is marked with reference number 33a. The rectangular building unitshown in FIG. 9f has two cavities 34a and 34b. Naturally the productionof hollow building units requires a suitable mould to form the cavities;the construction of the mould structure for the building elementaccording to FIG. 9f is shown in FIG. 10. Ducts and holes are formed inthe outer mould frame 34 as well as in the walls of the hollow internalmould cores 36, 37 (the cavities are marked with reference numbers 36aand 37a)--similarly as shown in FIGS. 3a, 3b--for injection of the CO₂gas, or for putting it through the material passing through the mould. Apossible way of having the gas flown is shown in FIG. 1 by arrows, butfor the better overview, illustration of the ducts and holes is omitted.

Moreover, the amount of CO₂ gas required for carbonation is alwaysproportionate to the quantity of cement used according to the givenformula, making out about 8-10 mass % thereof. The gas mixture used forcarbonation--if not pure CO₂ is used--should contain expediently atleast 30% of CO₂.

The invention is described in further details by way of examples asfollows:

EXAMPLE 1

20 mm thick, 60×100 cm building panels are produced with the processaccording to the invention using the apparatus shown in FIGS. 1 and 2.Composition of the raw afterhardening mixture to be moulded by pressingand treated with carbonation is the following:

    ______________________________________                                        cement              42    mass %                                              caustic lime        2     mass %                                              quartzsand          42    mass %                                              water               14    mass %                                              ______________________________________                                    

FIG. 4 illustrates the trend of the internal stress (pressure) P and thedensity R_(o) as a function of the time consequent upon compression inthe mixture not containing elastic (organic) additive-component. In theinitial phase of the pressing process both the internal stress and thedensity are rapidly increasing, but after a short time, increase of thedensity slows down, the curve R_(o) is nearly parallel to the axis oftime (it hardly approches to the latter) while the internal stress Pupon reaching a maximum, remains essentially constant for a short time,then it rapidly drops. The internal stress at the intersection M of thecurves P and R_(o) is only as high, at which the density R_(o) of themixture practically would not change even if the compressive force wasstopped. (Moreover, the pressure and density of all those afterhardeningmixtures are characterized by curves similar to the graph in FIG. 4, themoisture content of which is at most 50% and their additives areinorganic, rigid materials e.g. sandy gravel, gravel, siliceous earth,fibreglass etc.).

The pressure conditions--i.e. trend of the internal stresses--as afunction of the time, arising while pressing in the mixture described inthis example, with the reciprocating piston 8 of the apparatus as shownin FIGS. 1-3, are illustrated with the set of curves according to FIG.6. Each curve P represents the internal stress-influence line of thecompression performed with each piston stroke. FIG. 6 clearly shows thatin the uppermost layer of the mixture in the mould space 5 (FIG. 1)always the same--and maximum--internal stress prevails, and it existscontinuously, because the upper horizontal parts of the curves P (seealso FIG. 4) are

DETAILED DESCRIPTION OF THE INVENTION practically passing into oneanother. Thus, as a result of the mechanical pressing process in thisupper layer of the material, the quasi gastight condition is ensureduntil the piston 8 of the apparatus stamps the mixture into the mould 1.

The CO₂ gas is injected into the material being present in the mould 1and moving downwards in zones I-III under the following pressure:

    ______________________________________                                        Zone I:      entry        6     bar                                                        exit         3     bar                                           Zone II:     entry        2     bar                                                        exit         1     bar                                           Zone III:    entry        0.4   bar                                                        exit         0     bar                                           ______________________________________                                    

The gas incidentally flowing down from zone III along the inner faces ofthe mould plates is emitted in the balancing zone IV; the amount of gasmay be only at minimum.

The material passes through the mould space 5 continuously at a rate of1.0 m/sec.

The gas pressure, path and time diagram in FIG. 8--where v is thevelocity of the material moving down in the mould, R_(o) is the densityof the afterhardening mixture, and d is the thickness of the producedbuilding panel--proves that the material passes through zone I--wherethe pressure of CO₂ gas is at the maximum (6 bar)--in about two minutes,whereas its passage through the zones I and II takes barely one minute,while the gas pressure gradually drops to zero, and the gas do not hasany overpressure in zone IV. The curve in FIG. 8 represents the internalrelaxation force proportional to the compressive force produced by thepiston, in other words, the intensity of the force required forcompaction and passing on the material to be pressed is alwaysproportional to the relaxation force affecting the sides of the mould.

The bending strength of the material leaving through the outlet port 7of the mould 1 is about 35 kp/cm² (about 30% of the final,28-day-strength), and its density is 1250 kg/m³. The panel materialcontinuously leaving the mould is cut according to the planned size witha cutting disc. The panels partly hardened by carbonation are storedstanding on their edge.

EXAMPLE 2

14 mm thick, 163×1250×4000 mm hollow building units are produced with heprocess according to the invention using the apparatus as shown in FIG.1-3. Composition of the raw afterhardening mixture to be shaped bypressing and treated by carbonation is the following:

    ______________________________________                                        cement              58    mass %                                              waterglass          1     mass %                                              woodshavings        14    mass %                                              water               24    mass %                                              caustic lime        3     mass %                                              ______________________________________                                    

FIG. 5 illustrates the trend of internal stress (pressure) P and densityR_(o) as a function of the time consequent upon compression of suchmixture--not containing any elastic (organic) additive-component.(Similar curves are obtained if instead of woodshavings other elastic,organic additive-components, e.g. cellulose, vegetable fibres, vegetablescrapings, synthetic fibres, etc., or a mixture containing theiroptional combination are used for preparation of the mixture.) In thiscase, the internal stress P--upon reaching a maximum value and when thecorresponding horizontal or essentially horizontal curve-section islonger than the corresponding part of curve P in FIG. 4--drops only at aslow rate, maintaining the compressive force over a longer time isrequired to keep the density R_(o) on a constant value. When thecompressive force is stopped (before hardening of the material) theinternal stress existing in the mixture would result in a decrease ofthe density, because the material would spring back (relaxation effect).

If the raw mixture of above composition was pressed into the mould 1with the reciprocating piston 8 of the apparatus shown in FIGS. 1 and 2,the pressure conditions according to FIG. 7 develop in the mixture. Thehorizontal section of the internal stress-influence lines Pcorresponding to each piston stroke in this case, too will passcontinuously into one another, i.e. always the same, maximum stress willprevail in the mixture in the vicinity of the inlet port 6 of the mouldspace 5 until the material is continuously stamped by the piston 8 intothe mould 1. This way, due to the mechanical compaction, the quasigastight condition is ensured during the process of production.

Pressure of the gas injected into and emerging from the zones I-III isthe same as the one shown in Example 1 and also the gas pressure, pathand time diagram is similar to that of FIG. 8, however, the volumeweight and strength of the end-product--consequent upon the differenceappearing in the additive--are lower.

The main advantage of the invention is that it enables continuously thelarge-scale production of building units, the strength of which, whendischarged from the mould, is at least 30% of the final (28-day)strength, thus, their production is extremely efficient and economical.A further advantage is the simplicity of the apparatus according to theinvention, consequently is cost of investment is relatively low, and itis suitable for the production of units from a raw mixture containingeither elastic (fibrous), or solid granular additive.

Naturally, the invention is not limited to the above described examplesof the process and to the illustrated and explained embodiments of theapparatus, but it can be realized in many ways within the protectivescope defined by the claims. The mould should not necessarily be of anupright position, the building units may be produced also in an inclinedor even in a horizontal mould. The process can be realized according toseveral formulae different from those described in the examples. Themethod of passing the gas through the material in motion is realizablein many ways different from the one described in the foregoing deviationfrom those described above is conceivable according to several otheraspects, without overstepping the protective scope defined by theclaims.

What we claim is:
 1. Apparatus for the production of building units froman afterhardening mixture containing cement and water as bindingmaterial wherein said binding material is hardened by carbonation, saidapparatus comprising a die comprising a die space, a CO₂ gas-sourcebeing capable of fluid communication with said die space, and holes inat least one wall of the die, said holes being suitable for injection ofCO₂ gas into the die space at pressure which exceeds the atmosphericpressure, the die having an inlet port for admitting the rawafterhardening mixture, and an outlet port for discharging the buildingunits hardened by carbonation; a press mechanism being situated in frontof the inlet port for pressing the raw afterhardening mixture into thedie space and moving the afterhardening mixture as well as the buildingunits hardened therefrom by carbonation through the die space; and theholes leading into the die space serving as inlets for the CO₂ gas, saidholes being divided into separate zones of hole groups and communicatingwith gas injection devices which include control means for separatelycontrolling the amount of CO₂ gas to be injected at each of said zones.2. Apparatus according to claim 1 wherein discharge holes are providedin at least one wall of the die for collecting the CO₂ gas remainingafter the completed carbonation reaction, said discharge holesexpediently communicating with pipes connecting the CO₂ gas-source, adie plate containing the holes for injecting CO₂ gas into the die space.3. Apparatus according to claim 2 wherein a forward pipe for injectingCO₂ gas into the die space, and a return pipe for recirculating into theforward pipe the CO₂ gas remaining after the completed carbonationreaction; a gas pump connected to the forward pipe into which the returnpipe also leads, and a pipe leading out of the CO₂ gas-source fittedwith shut-off means and being joined to the return pipe; and the forwardpipe being interconnected through inlet leg pipes containing valves tosaid hole zones on the gas-injection side of said die space, outlet legpipes fitted with valves leading from the die space into the return pipebeing provided for discharging the gas remaining after the completion ofthe carbonation reaction.
 4. Apparatus according to claim 3 wherein avacuum pump is inserted into the return pipe.
 5. Apparatus according toclaim 3 wherein the hole groups on both the gas inlet side and theremaining-gas outlet side lead into separate closed chambers fitted in agastight manner to the outer face of the die plates.
 6. Apparatusaccording to claim 3 wherein the hole groups are leading from ductsrunning inside the die plates into the die space, each ductcommunicating with one of the leg pipes leading out of the forward pipe,and with one of the leg pipes leading into the return pipe,respectively.
 7. Apparatus according to claim 1, including a saw meansbeing provided behind the outlet port of the die for cutting up thecarbonation-hardened material into units as the material leaves the diespace.
 8. Apparatus according to claim 1 wherein chambers cover at leastone of the hole groups and are fitted to the outer side of the dieplates in the vicinity behind the outlet port of the die.
 9. Apparatusaccording to claim 1 wherein the press mechanism contains areciprocating piston, the cross sectional shape and size of which areapproximately the same as those of the inlet port of the die. 10.Apparatus according to claim 9 wherein the die is of verticalarrangement, the piston being fitted between guide rails and the guiderails being covered with a bell-shaped protective cover, a lower flangeof said cover being in the vicinity of the lower edge of the guiderails; and an opening provided between said lower flange and the guiderails; and the mechanism together with the protective cover beingsituated in a hopper for feeding the raw afterhardening mixture into thedie, said hopper leading to the upper end of the die space.